Stabilized polyacrylonitrile compositions and method of forming same

ABSTRACT

A METHOD OF FORMING STABILIZED POLYACRYLONITRILE COMPOSITIONS WHICH ARE PARTICULARLY SUITED FOR THE SPINNING OF POLYACRYLONITRILE FIBERS AND FILMS AND THE COMPOSITIONS PRODUCED THEREBY WHEREIN ACRYLONITRILE POLYMERS CONTAINING AT LEAST 85 PERCENT ACRYLONITRILE ARE DISSOLVED IN A SOLVENT CONTAINING AN UNSATURATED HYDROCARBON AS A COLOR STABILIZER, WHICH SOLVENT IS ACETONITRILE OR AN ACETONITRILE/WATER MIXTURE. PREFERABLY, THE SOLVENT AND POLYMER ARE PURGED WITH NITROGEN AND THE PH OF THE SOLVENT IS ADJUSTED TO ABOUT 6.0-7.0.

STABILIZED POLYACR SELONITRILE COMPOSI- TIONS AND METHOD OF FORMING SAMEDarrell R. Thompson, Somerville, N.J., and Michael W.

Ensley, Charlotte, NC, assignors to Celanese Corporation, New York, NY.

No Drawing. Filed Apr. 22, 1971, Ser. No. 136,622

Int. Cl. C08f 45/24 U.S. Cl. 260-296 AN 14 Claims ABSTRACT OF THEDISCLOSURE A method of forming stabilized polyacrylonitrile compositionswhich are particularly suited for the spinning of polyacrylonitrilefibers and films and the compositions produced thereby whereinacrylonitrile polymers containing at least 85 percent acrylonitrile aredissolved in United" States Patent a solvent containing an'unsaturatedhydrocarbon as a color stabilizer, which solvent is acetonitrile or anacetonitrile/water mixture. Preferably, the solvent and polymer arepurged with nitrogen and the pH of the solvent is adjusted to about6.0-7.0.

BACKGROUND OF THE INVENTION This invention relates to the stabilizationof polyacrylonitrile compositions. More particularly, the inventionrelates to the stabilization of polyacrylonitrile compositionscontaining a low-boiling solvent, which compositions are particularlyuseful for the formation of shaped articles'such asfibers and films andwhich have a tendency to develop color either upon standing or upon theapplication of heat.

The terms polyacrylonitrile and acrylonitrile polymers as used hereinrefer to homopolymers as well as copolymers of acrylonitrile containingat least 85 percent by weight acrylonitrile and up to about 15 percentby weight of at least one other ethylenically unsaturated compoundcopolymerizable with acrylonitrile.

The utility of acrylonitrile polymers is well-established,

particularly'for the preparation of such shaped articles as fibers andfilms. However, preparative techniques generally are restricted to dryspinning and wet spinning from solutions having a polymer concentrationup to about 25 to 40 percent by weight. Conventional spinningtechnology, dry spinning in particular, has utilized relativelyhighboiling solvents, e.g., boiling above about 100 degrees centigrade,for forming spinnable dopes of acrylonitrile polymers. The formation ofshaped articles by a melt extrusion process, that is, a process in whichthe polymer is melted and the molten polymer extruded through a die orspinnerette into an inert medium in contradistinction to dry and wetspinning methods in which a so lution of the polymer is extruded througha die or spinnerette, is not practical because of the relatively highmelting temperatures of acrylonitrile polymers containing at least 85percent by weight acrylonitrile and because of the tendency of suchpolymers to decompose before or during melting.

Acrylonitrile polymers having an acrylonitrile content of at least 85percent generally are insoluble in the more common solvents. Wheneversuitable solvents have been found, however, the application of heatusually is necessary in order to effect solution. The application ofheat to effect solution usually results in the development of a paleyellow color in the resultant solution, which color generally darkensand becomes brown with time. Even without the application of heat orupon removal of heat after a solution has been obtained, color developsin solutions upon standing for prolonged periods of time. Colordevelopment is more pronounced at elevated temperatures and in thepresence of bases or other strong nucleophiles.

Color development is most severe in N,N-dimethylformamide solutions suchas those employed in dry spinning. Obviously, any color developed inpolymer solutions or spinning dopes will be carried over into theproducts formed therefrom.

The mechanism responsible for color formation and the nature of thechromophores involved still are uncer tain. The color may be caused bythe presence of metal ions such as iron, copper, and manganese in thepolymer solutions. Impurities other than metal ions present in thesolvents also have been cited as a cause. The'em-' ployment of amides,such as N,N-dimethylformamide, as solvents may result in the thermaldecomposition of the solvent to give amines which in turn may causecolor formation. Or, color formation may be caused by con jugation ofcarbon-nitrogen double bonds derived from the cyanide groups in thepolyacrylonitrile. Such conjugated double bonds conceivably may resultfrom a cyclization reaction initiated by oxidation products, such ashydroperoxides, in the polymer. The resultant conjugated structureswould be colored because of the low energy electronic transitionspossible in the resonating double bond system. Regardless of themechanism which gives rise to color in solutions of acrylonitrilepolymers, e.g., spinning dopes, the presence of color in polymersolutions results in shaped articles which are colored. Such colorationis undesirable for aesthetic reasons and Ice contributes to productnon-uniformity.

SUMMARY OF THE INVENTION It is therefore an object of the presentinvention to provide stabilized polyacrylonitrile compositionscontaining a low-boiling solvent.

It is another objects to prevent undesirable color formation inpolyacrylonitrile compositions containing a low-boiling solvent.

Still another object of the present invention is to minimize colorformation in polyacrylonitrile compositions containing a low-boilingsolvent when such compositions either are permitted to stand forprolonged periods of time or are heated, either to effect solution ofthe polyacrylonitrile in the solvent or during spinning of saidcomposition to provide shaped articles.

Yet another object is to provide stabilized polyacrylonitrilecompositions containing a low-boiling solvent from which crystal-clearshaped articles may be prepared wherein clarity and freedom from colorare independent of thickness, fiber denier, or the like. i

It is also an object of the present invention to provide a method forpreparing stabilized polyacrylonitrile compositions containing alow-boiling solvent, which compositions are particularly suited for theformation of shaped articles of polyacrylonitrile. 1

Yet another object is to provide a method for prepar ing stabilizedpolyacrylonitrile compositions containing a low-boiling solvent, whichsolvent is acetonitrile or an acetonitrile/Water mixture and whichcompositions can, if desired, be stored or shipped as a solid or gelledmaterial and subsequently formedinto a spinning solution g; dope for thepreparation of polyacrylonitrile fibers and These and other objects willbe apparent to those skilled in the art from a consideration of thedescription and claims of the invention which follow. A

In accordance with the present invention, stabilized polyacrylonitrilecompositions containing a low-boiling solvent are obtained by theprocess which comprises the steps of adding a minor amount of anunsaturated hydrocarbon or allyl ether stabilizer to a solvent which isacetonitrile or an acetonitrile/Watermixture containing up to about 50weight percent water, adding acrylonitrile polymer to thesolvent-stabilizer mixture, heating and mixing thepolyacrylonitrile-solvent-stabilizer mixture under superatmosphericpressure to a temperature above about the boiling point at atmosphericpressure of said solvent and below the degradation temperature ofthepolyacrylonitrile, i.e., within the range from about 80 to 160degrees centigrade, to produce a solution. The resultant solution thencan be cooled to a temperature below its original solubilizingtemperature and above about the boiling point at atmospheric pressure ofsaid solvent without gelation occurring. Cooling the resultant solutionto a temperature below about the boiling point at atmospheric pressureof said solvent, e.g., to ambient temperature, results in the gelationof said solution. Preferably, the stabilizer is added to saidsolventprior to the addition of the polyacrylonitrile to said solvent.Also, the solvent and polyacrylonitrile preferably are purged separatelywith nitrogen and the .pH of the solvent is adjusted to about 6.07.0.

While the present invention contemplates the use of acetonitrile aloneas solvent, it is preferred that an acetonitrile/ water mixture beemployed as solvent wherein said solvent contains up to about 45 to 50percent water, based on the weight of acetonitrile. Spinning solutionsof a stabilized polyacrylonitrile composition of the present inventionare obtained by maintaining said composition under sufficientsuperatmospheric pressure to permit the maintenance of said compositionat a temperature above the gel temperature of said composition withoutdistillation of said solvent, said gel temperature being near to butbelow the boiling point at atmospheric pressure of said solvent.

In general, the unsaturated hydrocarbon stabilizers of the presentinvention contain only hydrogen and carbon. Further, while a portion ofthe unsaturation present in any given stabilizer may be aromatic, thereis present in the stabilizer at least one non-aromatic carbon-carbondouble bond. More than one non-aromatic double bond may be present inthe stabilizer, provided that the molecular structure prevents migrationand conjugation of the non-aromatic double bonds.

DE'iAILED DESCRIPTION OF THE INVENTION As indicated hereinbefore,stabilized polyacrylonitrile compositions containing a low-boilingsolvent are obtained by the inclusion in said compositions of a minoramount of an unsaturated hydrocarbon. By a minor amount is meant lessthan about 10 percent, based on the weight of polyacrylonitrile, andpreferably less than about 5 percent. The most preferred range ofunsaturated hydrocarbon addition is from about 0.01 percent to about 3.0percent. Also as indicated hereinbefore, the unsaturated hydrocarbonstabilizers of the present invention, which stabilizers contain onlyhydrogen and carbon, may be aliphatic, alicyclic, or aromatic; ifaromatic, at least one non-aromatic carbon-carbon double bond must bepresent. Examples of the unsaturated hydrocarbon stabiilzers of thepresent invention include, among others, styrene, tbutylstyrene,cyclohexene, pinene, norbornene, camphene, bornylene, and the like.Preferred stabilizers include styrene, t-butylstyrene, cyclohexene, andpinene, with styrene and cyclohexene being most preferred.

As stated above, although the mechanisms involved are still uncertain,in addition to the afore-disclosed unsaturated aliphatic, alicyclic oraromatic hydrocarbon stabilizers having at least one non-aromaticcarboncarbon double bond; allyl ether has also been found to be aneffective color stabilizer for use in the instant invention.

The presence of said unsaturated hydrocarbon stabilizers inpolyacrylonitrile compositions containing a low-boiling solventeffectively minimizes color formation in said compostions, even whensaid compositions are exposed to heat. The effectiveness of saidstabilizers, however, may be improved by excluding oxygen from saidcompositions and by adjusting the pH of the solvent to about 6.0-7.0.

' vacuum chamber and the chamber evacuated. Nitrogen then is introducedinto the chamber. This procedure of evacuation and nitrogen purging isrepeated several times as necessary. The polymer and pH-adjustedsolution then are brought together and heated under a nitrogenatmosphere to effect solution. The resultant stabilizedpolyacrylonitrile composition then is either stored or used directly toprepare shaped articles.

In addition to the foregoing procedure for improving the effectivenessof the unsaturated hydrocarbon stabilizers of the present invention, theaddition to the solventstabilizer solution of a small'amount of what maybe termed a stabilizer enhancer often increases the effectiveness ofsaid unsaturated hydrocarbon stabilizers, said increase in effectivenessbeing distinctly separate from the increase in effectiveness resultingfrom the procedure of oxygen exclusion and solvent pH adjustment asdescribed hereinbefore. By the term stabilizer enhancer is meant acompound the use of which in conjunction with said stabilizers allowsreduced color formation when compared to the use of said stabilizersalone. An example of a stabilizer enhancer is sodium hydrogen sulfite.By a small amount is meant less than about 0.1 percent by Weight, basedon the amount of polyacrylonitrile.

As stated hereinbefore, the present invention is directed to theformation of stabilized polyacrylonitrile compositions wherein thepolyacrylonitrile contains at least percent acrylonitrile. Theseacrylonitrile polymers can be acrylonitrile homopolymers as well ascopolymers of two or more monomers wherein up to about 15 percent of thepolymer can be another ethylenically unsaturated compound which iscopolymerizable with acrylonitrile. Such materials, which can bemonomers or polymers which are copolymerizable with the acrylonitrile,usually are added to modify and/or enhance certain characteristics ofthe polyacrylonitrile or shaped articles made therefrom. Often thematerial copolymerized with the acrylonitrile contains a chemical groupwhich increases the basic dyeability of the resulting polymer. Suchdyeability-enhancing compounds normally contain sulfur or phosphorous inthe ethylenically unsaturated material copolymerizable with theacrylonitrile. Typically, such sulfuror phosphorous-containing compoundsare added in an amount of from about 0.1 to about 5 percent'by weight,based on the weight of the total polymer composition. Other modifyingsubstances usually are used in amounts up to about 15 percent. Typicalethylenically unsaturated monomers copolymerizable with acrylonitrileinclude,- among others, methyl acrylate, vinyl acetate, vinylidenechloride, methyl methacrylate, methallyl alcohol, vinylidene cyanide,styrene sulfonic acids, sodium methallylsulfonate, mixtures and partialpolymers thereof, and the like, all of which are well known to thoseskilled in the art. Similarly, acid dyeability may be imparted to thepolyacrylonitrile by the use of amine-containing comono mers such asallylamine. The polymers are obtained by conventional methods which arewell known in the art.

The degree to which the polymer is polymerized is dependent upon the enduse for which the polymer is intended. Thus, for the spinning ofpolyacrylonitrile fibers, the polymer preferably is polymerized to aninherent viscosity, measured at 25 degrees centigrade indimethylformamide of from about 0.5 to about 2.5 and more preferablyfrom about 1.2 to about 1.8. Of course, polymers having higher inherentviscosities can be used, resulting in higher solution viscosities for agiven solvent concentration; higher inherent viscosities also may resultin a loss or reduction of certain desirable properties, such as abrasionresistance, fibrillation, and the like.

In most instances wherein the present compositions are most desirablyused, solutions having a high concentration of solids are preferred.With the present solvent system and process, solutions having a highconcentration of solids are readily obtained with acrylonitrile polymershaving inherent viscosities in the range normally used for commercialfiber spinning, i.e., from about 1.2 to about 1.8. In particular,solutions having a solids content of from about 30 to about 70 percentby weight are readily obtained. The more preferred spinning solutionshave a solids content in the range of from about 35 to about 55 percentwith polymers having inherent viscosities of from about 1.2 to about 1.8or higher. With polymers having lower inherent viscosities, e.g., fromabout 0.5 to about 1.2, solutions having a solids content of up to about70 percent or higher can be obtained.

The solvent may be acetonitrile alone or more preferably anacetonitrile/water mixture. The addition of water to acetonitrile lowersboth the gel temperature of the polymer solution and the initialsolution temperature of the polymer. Therefore, in the solvent portion,it is preferable to use up to about 50 weight percent of water based onthe weight of acetonitrile, more preferably from about 2 to about 40weight percent water, and most preferably from about 18 to about 35weight percent water. In the most preferred range of water content, thelowest solution viscosities for a given polymer are obtained.

At atmospheric pressure, the boiling point of acetonitrile is about 82degrees centigrade and that of the azeotrope of 15 percent water isabout 76 degrees centigrade. To form the initial solution, temperaturesin excess of the boiling temperature of acetonitrile are used,particularly for the more diflicultly soluble acrylonitrile polymers.Consequently, the process is operated under superatmospheric pressurewhich can be either an applied pressure or the solvent vapor pressurewhich is developed autogenously at the elevated temperatures. Thepressure employed preferably is that required to maintain the solventprimarily in the liquid phase at the solvating temperature. Thisrequired pressure increases with increasing temperature and is in therange of about 30 to about 40 pounds per square inch gauge at about 100degrees centigrade. Thus, solvation preferably is conducted in apressure unit or sealed system to prevent the escape of solvent vaporand to maintain the solvent in the liquid phase.

The solvation temperature required to obtain the compositions of thepresent invention will vary with the proportions of acetonitrile andwater and with the proportion and kind of polyacrylonitrile, within therange of from about 80 to about 160 degrees centigrade. Once solvationis attained, however, the temperature of the composition can be reducedto the desired holding or spinning temperature. Reducing the temperatureof the composition below about 80 degrees centigrade, again dependingupon the nature of the composition, results in the gelling of thecomposition. Accordingly, the composition can be either cooled andretained in a gelled state for storage or shipment or maintained in thetemperature range of from about 80 degrees centigrade to the degradationtemperature of the polymer. If the composition is stored as a gel, it ispreferred to retain the composition in a sealed container to reduce oreliminate the gradual loss of solvent therefrom over a period of time.

It may be pointed out that the compositions of the present invention areremarkably stable to prolonged heating. By way of illustration, acomposition consisting of 40 weight percent of a polyacrylonitrilecomprised of 95 percent by weight of acrylonitrile and 60 weight percentof an acetonitrile/water mixture containing 22 percent 6 water showspractically no change in viscosity after three days at 100 degreescentigrade.

The following examples will serve to illustrate the invention Withoutintending to limit it in any manner:

EXAMPLE 1 To an autoclave having a stirring means and a heating meansand fitted with a condenser and a nitrogen inlet tube extending to thebottom of the vessel are added 60 parts of a solvent consisting ofpercent by weight acetonitrile and 20 percent by weight water and 0.2part (0.5 weight percent, based on the weight of polyacrylonitrile) ofstyrene. The mixture is stirred at ambient temperature until a solutionis obtained. The pH of the resulting solution is adjusted to about6.0-7.0 by the drop-wise addition of concentrated sulfuric acid.Nitrogen then is bubbled slowly through the solution to displacedissolved and atmospheric oxygen. During this time, a vacuum chamber ischarged with 40 parts of polyacrylonitrile powder characterized asfollows: 7

percent polyacrylonitrile 4.8 percent methyl acrylate 0.2 percent sodiummethyl allyl sulfonate The vacuum chamber is evacuated and nitrogenintroduced until atmospheric pressure is attained. Theevacuationnitrogen introduction cycle is repeated two more times. Thepolyacrylonitrile powder then is charged to the autoclave under anitrogen purge. While maintaining a nitrogen atmosphere in theautoclave, the polymer-solvent mixture is heated at 85 degreescentigrade and under a pressure of 2500 mm. mercury for 0.5 hour. Theresultant solution has a color rating of 4 after 24 hours at degreescentigrade and is comprised of 40 percent solids.

Color rating is determined by comparing the polymer solution with aseries of color tubes containing increasing concentrations of ayellow-brown dye, Irgacet Yellow ZRL, in N,N-dimethylformamide. Tubenumber 1 contains only solvent. Tube number 2 contains 1.0)(10 percentby weight of the dye. The concentration of dye in each succeeding tubeincreases by 1.0X10- weight percent, so that the dye concentration inany given tube is given by (tube numberl) 10- weight percent.

For control purposes, the procedure of Example 1 is repeated, exceptthat styrene addition, pH adjustment, and oxygen exclusion are omitted.After 24 hours at 110 degrees centigrade, the polymer solution has acolor. rating of 41.

EXAMPLE 2 The procedure of Example 1 is repeated, except that oxygenexclusion is omitted. After 24 hours at 110 degrees centigrade, thepolymer solution has a color rating of 5.

EXAMPLE 3 The procedure of Example 1 is repeated, except that pHadjustment is omitted. After 24 hours at 110 degrees centigrade, thepolymer solution has a color rating of 5.

EXAMPLE 4 The procedure of Example 3 is repeated, except that the amountof styrene is decreased to 0.1 weight percent. After 24 hours at 110degrees centigrade, the polymer solution has a color rating of 6.

EXAMPLE 5 The procedure of Example 3 is repeated, except that the amountof styrene is decreased to 0.05 weight percent. After 24 hours at 110degrees centigrade, the polymer solution has a color rating of 6.

EXAMPLE 6 The procedure of Example 1 is repeated, except that pHadjustment and oxygen exclusion are omitted. After 24 hours at 110degrees centigrade, the polymer solution has a color rating of 7.

7 EXAMPLE 7 The procedure of Example 6 is repeated, except that 0.02weight percent of sodium hydrogen sulfite as a stabilizer enhancer isadded. The polymer solution is slightly turbid and has a color rating of4 after 24 hours at 110 degrees centigrade.

EXAMPLE 8 The procedure of Example 6 is repeated, except that thestyrene is replaced with an equal amount of cyclohexene. The polymersolution is slightly turbid and has a color rating of 9 after 24 hoursat 110 degrees centigrade.

EXAMPLE 9 The procedure of Example 8 is repeated, except that thestyrene is replaced with an equal amount of cyclohexene and the pHadjustment is omitted. After 24 hours at 110 degrees centigrade, thepolymer solution has a color rating of 4.

EXAMPLE 10 The procedure of Example 1 is repeated, except that thestyrene is replaced with an equal amount of pinene. After 24 hours at110 degrees centigrade, the polymer solution has a color rating of 6.

EXAMPLE 11 The procedure of Example 3 is repeated, except that thestyrene is replaced with an equal amount of pinene. After 24 hours at110 degrees centigrade, the polymer solution has a color rating of 6.

EXAMPLE 12 The procedure of Example 6 is repeated, except that thestyrene is replaced with an equal amount of allyl ether. After 24 hoursat 110 degrees centigrade, the resulting solution has a color rating of16.

EXAMPLE 13 The procedure of Example 6 is repeated, except that thestyrene is replaced with an equal amount of t-butylstyrene. After 24hours at 125 degrees centigrade, the polymer solution has a color ratingof 11.

As a control, the procedure of Example 13 is repeated, except that theaddition of t-butylstyrene is omitted. After 24 hours at 125 degreescentigrade, the polymer solution has a color rating of 71.

EXAMPLE 14 The procedure of Example 6 is repeated. After 24 hours at 135degrees centigrade, the polymer solution has a color rating of 16.

EXAMPLE 15 The procedure of Example 6 is repeated, except that theamount of styrene is increased to 1.0 weight percent. The resultingsolution is slightly turbid. After 24 hours at 135 degrees centigrade,the polymer solution has a color rating of 11.

EXAMPLE 16 The procedure of Example 6 is repeated, except that theamount of styrene is increased to 2.0 weight percent. The resultingsolution is slightly turbid. After 24 hours at 135 degrees centigrade,the polymer solution has a color rating of 7.

From a reading of the present disclosure, various changes andmodifications in the disclosed process will be obvious to those skilledin the art. For example, the pH adjustment of the solvent may beaccomplished by the addition of mineral acids other than sulfuric acidor by the addition of anhydrides of mineral acids. The pH adjustment ofthe solvent also may be accomplished by the use of organic acids, suchas carboxylic acids (e.g., acetic acid) and sulfonic acids.Alternatively, solvent pH control may be accomplished by the use ofbases such as sodium hydroxide or buffers of various types. Furthermore,exclusion of oxygen from the solvent may employ reduced pressures inconjunction with nitrogen purging. These and other changes andmodifications by those skilled in the art are considered to be withinthe spirit and scope of the present invention.

Throughout the foregoing disclosure and the claims which follow, thecompositions of the present invention are referred to as solutions of apolymer in a solvent. However, the exact nature of said compositions isnot known. It does appear, though, that the acetonitrile portion of thesolvent is absorbed by the polymer to fiuidize it, rather than thepolymer being dissolved in the solvent. Thus, at least in someinstances, said compositions may deviate from typical solutions. In viewof the uncertainties involved, the terminology employed is consideredsatisfactory since such terminology enables any person skilled in theart to make and use said compositions.

Having thus disclosed the invention, what is claimed is:

1. A stabilized film or fiber forming polyacrylonitrile compositionconsisting essentially of polyacrylonitrile containing at least percentacrylonitrile and up to about 15 weight precent of at least one otherethylenically unsaturated material copolymerized therewith having addedthereto a solvent which comprises acetonitrile containing up to about 50percent water and from about 0.01 to 3 weight percent, based on theweight of said polyacrylonitrile of unsaturated aliphatic, alicyclic oran aromatic hydrocarbon stabilizer having at least one non-aromaticcarbon-carbon double bond or allyl ether.

2. The stabilized polyacrylonitrile composition of claim 1 wherein saidpolyacrylonitrile consisting essentially of from about 30 to about 70percent of said composition.

3. The stabilized film or fiber forming polyacrylonitrile composition ofclaim 1 wherein said stabilizer is selected from the group consisting ofstyrene, t-butylstyrene, cyclohexene, allyl ether, and pinene.

4. The stabilized film or fiber forming polyacrylonitrile composition ofclaim 1 wherein said solvent contains from about 2 to about 40 percentwater and said stabilizer is selected from the group consisting ofstyrene, t-butylstyrene, cyclohexene, allyl ether, and pinene.

5. The stabilized film or fiber forming polyacrylonitrile composition ofclaim 4 wherein said polyacrylonitile is a homopolymer.

6. The stabilized film or fiber forming polyacrylonitrile composition ofclaim 4 wherein at least one of said ethylenically unsaturated materialsis a sulfur-containing material.

7. The stabilized film or fiber forming polyacrylonitrile composition ofclaim 4 wherein at least one of said ethylenically unsaturated materialsis methyl acrylate.

8. A stabilized film or fiber forming polyacrylonitrile compositionconsisting essentially of from about 30 to about 70 percent ofpolyacrylonitrile containing from 85 to about 99 percent acrylonitrile,from about 0 to about 15 percent of an ethylenically unsaturatedmaterial 00- polymerized therewith, and from about 0.1 to about 2percent of a sulfur-containing ethylenically unsaturated material alsocopolymerized therewith; having added thereto from about 29 to about 60percent of a solvent consisting of acetonitrile and from about 2 toabout 40 percent water; and from about 0.01 to about 3 Weight percent,based on the Weight of said polyacrylonitrile, of a stabilizer selectedfrom the group consisting of styrene, t-butylene styrene, cyclohexene,allyl ether, and pinene; said composition being maintained undersuperatmospheric pressure greater than about the vapor pressure of saidsolvent and at a temperature at from about 80 to about degreescentigrade.

9. A method of forming stabilized film or fiber formingpolyacrylonitrile compositions which comprises the steps of adding fromabout 0.01 to about 3 weight percent, based on the weight of saidpolyacrylonitrile of an unsaturated aliphatic, alicyclic or aromatichydrocarbon stabilizer having at least one non-aromatic carbon-carbondouble bond or allyl ether to a solvent which comprises acetonitrilecontaining up to about 50 percent water adding polyacrylonitrile whichcontains at least 85 percent acrylonitrile and up to about 15 weightpercent of at least one other ethylenically unsaturated materialcopolymerized therewith, and heating and mixing the resultant mixtureunder superatmospheric pressure to a temperature above about 80 degreescentigrade and below the degradation temperature of saidpolyacrylonitrile to produce a solution.

10. The method of claim 9 wherein said stabilizer is selected from thegroup consisting of styrene, t-butylstyrene, cyclohexene, allyl ether,and pinene.

11. The method of claim 9 wherein said superatmospheric pressure isgreater than the vapor pressure of said solvent.

12. The method of claim 9 wherein oxygen is excluded and the pH of thesolvent is adjusted to about 6.0-7.0.

13. The method of claim 9 wherein said polyacrylonitrile makes up fromabout 30 to about 70 percent of said compositions.

14. A method of forming stabilized film or fiber formingpolyacrylonitrile compositions which comprises the steps of adding fromabout 0.01 to about 3 weight percent, based on the weight ofpolyacrylonitrile, of a stabilizer which is selected from the groupconsisting of styrene, t-butylstyrene, cyclohexene, allyl ether, andpinene to a solvent which consists of acetonitrile and from about 2 toabout percent water; adjusting the pH of the resulting solution to about6.0-7.0; purging the resulting solution with nitrogen to excludedissolved and atmospheric oxygen; adding polyacrylonitrile containing atleast 85 percent acrylonitrile and up to about 15 weight percent of atleast one other ethylenically unsaturated material 00- polymerizedtherewith, wherein said polyacrylonitrile has been purged with nitrogen;and heating and mixing the resultant mixture in nitrogen atmosphereunder superatmospheric pressure which is greater than the vapor pressureof said solvent and at a temperature above about degrees centigrade andbelow the degradation temperature of said polyacrylonitrile.

References Cited UNITED STATES PATENTS 3,574,177 4/1971 Nakajima et al.260-296 AN 2,525,521 10/ 1950 Caldwell 260-296 AN 3,194,862 7/1965Coover et a1. 260-296 AN 3,632,543 l/ 1972 Nakanome et a1. 260-296 ANHAROLD D. ANDERSON, Primary Examiner US. Cl. X.R.

260-296 MH, 29.6 ME, 32.4

